Generally, the present invention is directed to methods and apparatus for hazardous gas detection. More particularly, the present invention is directed to systems for detecting hazardous gases in inclement environmental conditions which may include conditions such as rain, and directed fluid streams such as splashed or hosed water.
In many types of gas-detection systems for hazardous gases, such as combustible hydrocarbons and hydrogen sulfide, hazardous gas sensors are positioned at locations at which hazardous gas monitoring is necessary or appropriate. Such sensors typically interpose a porous metal flame arrestor between electrical gas sensor elements and the environment, for safety purposes. An output or controller device may be combined with the sensor, or may be positioned remotely from the sensor for monitoring the sensor output. Such sensors are conventionally located in and around factories, pilot plants, refineries and chemical process plants, where they may be continuously or intermittently subjected to undesirable environmental operating conditions such as dust, dirt, rain and directed fluid streams. In this regard, water sprays, mists or streams from repair, maintenance or cleaning operations, as well as leakage, breakdown or faulty operation of equipment or manufacturing processes may adversely affect the performance and reliability of a hazardous gas sensor unless the sensor is protected from such conditions. Similarly, hazardous gas sensors which are located in unprotected outside areas will be exposed to rain and other adverse environmental conditions which may also degrade or defeat sensor performance. Excessive moisture can damage gas sensors by causing the sensor to short, by causing thermal shock to sensors operated at elevated temperatures, by combining with corrosive gases to chemically attack the sensor, and may interact with ambient dust or dirt to permanently plug up porous flame arrestors which will inhibit sensor performance. Of course, water alone will typically fill the pores of the flame arrestor of a hazardous gas sensor having such an arrestor, thereby at least temporarily inhibiting sensor performance until it is dried from the arrestor Moreover, hydrogen sulfide sensors are adversely affected by moisture, which can defeat or degrade sensor performance. As indicated, hazardous gas sensors should be protected from such excess moisture, which can temporarily or permanently interfere with the ability of such sensors to detect the presence, or measure the quantity of hazardous gas. However, because such sensors are intended to measure and detect hazardous gases, and because rapid sensor response to the environment is important for safety or process control reasons, it is important that sensor protective apparatus should not significantly interfere with free and ready access and exposure to the atmosphere in the zone to be protected by the sensor.
Typically, hazardous gas sensors are protected from fluid contamination or interference such as rain, splashed water or hosed water by protective splash guard devices made from a plurality of slotted tubes of varying diameters, arranged concentrically, with respective slots of adjacent consecutive tubes angularly displaced from each other, to present a cylindrical labyrinth passageway to water flow. Water entering the slots in an external tube may be deflected by the internally adjacent tube surface, and water passing through the internal tube slots may again be deflected by the next internally adjacent tube surface. Each deflection slows the water, so that it may drain from the bottom of the concentric tube splash guard before reaching the porous metal flame arrestor or hazardous gas sensor. However, conventional, concentric tubular splash guard devices may have a number of disadvantages. In this regard, if designed to permit rapid gas diffusion to the sensor, concentric tubular splash guard devices may not effectively keep water away from the sensor, and may be ineffective in protecting the sensor from water sprays or streams directed along the axes of the tubes. However, if such concentric slotted tube splash guard assemblies are designed to most effectively prevent water impingement on the sensor, the access of the sensor to the ambient atmosphere may be significantly impeded, and the time necessary for hazardous gas to diffuse around the labyrinth passageway to reach the sensor is increased, thereby increasing the time necessary for the sensor to be capable of detecting a hazard. Moreover, such concentric tube splash guard devices are typically designed to be screwed onto the sensor, which may present assembly or maintenance difficulties for hazardous gas sensors which are not positioned in readily accessible locations.
Accordingly, there is a need for improved hazardous gas sensor assemblies and sensor protection systems, and it is an object of the present invention to provide such improved hazardous gas sensor assemblies and sensor protection systems. These and other objects will be apparent from the following detailed description and the accompanying drawings.